Active site mapping studies on transglutaminases using model substrates will continue. Special emphasis is being placed on the blood coagulation transglutaminases (plasma and platelet factor XIII) using a series of glutamine-containing peptide derivatives of amino acid sequences known to occur in the cross-linking regions of mammalian fibrins. Selective limited cleavages of the transglutaminases are being carried out using chemical agents and proteolytic enzymes. Subunit structures, subunit dissociations, and reassociations are under investigation. The purpose of these studies is to relate the structure of the transglutaminases to their catalytic function and to determine the common structural features of these enzymes which have very similar catalytic functions and mechanisms.